The two primary channels of communication in primate species are the face and the voice. Normally, facial gestures and accompanying vocalizations provide highly redundant information because they are always spatially co-located, temporally synchronous, and specified by overlapping patterns of dynamic audible and visible information. Adults profit from the multisensory redundancy that vocalizing faces offer because they use the redundancy to integrate the separate auditory and visual streams of information into coherent perceptual experiences and because the redundancy makes it easier to detect, learn, and remember vocalizing faces. Although extant evidence indicates that the ability to take advantage of multisensory redundancy emerges early in infancy, the processes underlying its emergence are still poorly understood. Consequently, the current project investigates the development of face-voice integration in human infants and explores the novel idea that perceptual narrowing plays a critical role in the development of intersensory integration. This novel idea is based on a recent discovery by the PI & his colleagues that younger infants can integrate a broader range of faces and voices than do older infants. We have found that young infants can integrate nonnative faces and vocalizations (either monkey faces and their vocalizations or foreign visible and audible speech sounds) but that older infants do not. Our findings are striking because they are counterintuitive and contrary to predictions arising from extant theories of intersensory development. They are, however, consistent with a growing literature on narrowing effects in the speech, face, and music processing domains and suggest that narrowing is a pan-sensory, domain-general process. Consequently, the current project will investigate intersensory perceptual narrowing (IPN). It will be guided by 5 specific aims whose purpose will be to shed light on: (1) the role of temporal intersensory synchrony, configural processing, gestural features, and language-general processes in IPN, (2) the general nature of IPN by testing for it across different types of integration tasks, (3) the role of experience in IPN, (4) the separate contribution of unisensory perceptual processes to IPN, and (5) whether the sensitive period for IPN is affected by multisensory redundancy. We will use the intersensory matching technique to examine face-voice integration, the habituation/test method to investigate learning and discrimination of faces and voices, and measure infant visual attention to index responsiveness. By shedding light on the perceptual and experience-dependent mechanisms that underlie the development of face-voice integration in infancy, this project will provide insights into the emergence of a critical communicative skill that is essential to adaptive functioning at the perceptual, cognitive, and social levels. This, in turn, will provide insights into the etiology of various developmental disorders (e.g., autism) and will facilitate the development of better diagnostic tools for such disorders and help develop better intervention methods to ameliorate these disorders.